1. Technical Field
The present invention relates to a light source device and a projector.
2. Related Art
In a light source formed by a solid-state light source, a large number of light emitting devices are often connected to a power supply output in series and driven by current control. In this connection state, when one light emitting device fails in a state of opening between terminals, all normal light emitting devices connected in series cannot be driven. As measures against the problem, it is proposed to connect, in parallel to the light emitting devices, a Zener diode that operates at a voltage higher than a voltage across terminals during the driving of the individual light emitting devices (see, for example, JP-A-2011-222124 (Patent Literature 1) and JP-A-2009-59835 (Patent Literature 2)). In this case, when a light emitting device fails in an open mode, the Zener diode changes to an ON state to feed an electric current to the other series light emitting devices to thereby drive the solid-state light source.
When the Zener diode is used, heat radiation is necessary because the Zener diode generates heat. It is also conceivable to connect, instead of the Zener diode, in parallel to the light emitting devices, a self-on device such as a thyristor or a triac that starts operation at a voltage higher than the voltage across terminals during the driving of the individual light emitting devices. When the self-on device is used, heat generation is small compared with the Zener diode. However, the self-on device involves a sudden drop of the voltage across terminals during the operation. Therefore, a large rush current flows from a driving power supply side to a light emitting device. When the driving is stopped once, a short-circuit protection device returns to an OFF state. When the light emitting device is driven again, the short-circuit protection device changes to the ON state again and the rush current flows. The repetition of the rush current causes deterioration of the other normal light emitting devices. In particular, for example, when PWM driving is performed for dimming, since the rush current flows at every PWM driving pulse, the deterioration of the light emitting devices is serious.